This application claims priority to Japanese Patent Application Nos. 2001-377670 and 2001-377651, both filed on Dec. 11, 2001.
1. Field of the Invention
The present invention relates to a radar data processing apparatus and data processing method for calculating the distance and relative velocity of a target based on peak data output from a radar apparatus, and for outputting data representing the results.
2. Description of the Related Art
A millimeter-wave radar (FM-CW radar) projects forward a continuous wave beam frequency-modulated by a triangular wave increasing and decreasing alternately in a cyclic fashion, receives an echo signal from a target, and produces a beat signal by mixing the echo signal with a portion of the transmitted signal; then, peaks appearing in the frequency spectrum of the beat signal are paired up between the increasing section and the decreasing section of the frequency modulation (hereinafter called the pairing), and the distance and the relative velocity of the target are calculated from the sum of, and the difference between, the frequencies of the paired peaks. Further, by physically or electronically scanning the beam projection angle, the direction in which the target is located can be determined. It is also possible to determine the absolute speed of the target, and more specifically, whether the target is stationary (a stationary target) or moving (a moving target), by knowing the traveling speed of the radar-equipped vehicle using a vehicle speed sensor.
In the above pairing process, between the peaks (up peaks) in the beat signal (up beat) during the increasing part of the frequency modulation and the peaks (down peaks) in the beat signal (down beat) during the decreasing part thereof, peaks close in angle and intensity are paired together as peaks occurring due to the same target.
Further, in order to determine each individual target, data continuity is checked by comparing the present data with the past data and determining whether the data are data obtained from the same target. For example, if a certain object has been recognized more than a predetermined number of times within a predetermined period of time, then the object is determined as being an eligible target.
Roadside objects installed at closely spaced intervals, such as guardrail posts, cause many reflections in rapid succession. In this case, as many peaks close in intensity appear within a narrow angle range, mispairing tends to occur in which peaks caused by different targets are paired up. Further, in the case of a moving target such as a large truck having many reflecting points at its rear end, such as tires, a car carrier, etc., many peaks tend to occur within a narrow angle range, which can also result in mispairing. Also, in the case of different targets, mispairing tends to occur if they are close in angle.
Further, if the radar beam hits a target after being reflected by a roadside wall or like structure, a mirror ghost occurs. If such a mirror ghost occurs, it may be erroneously determined in the continuity check that there is continuity between the real target in the past data and the mirror ghost in the present data, resulting in an inability to check the continuity of the real target in the present data, or an erroneous calculation of the lateral position of the target with the real target being united with the mirror ghost.
In the continuity check where the present data is compared with the past data to determine whether the data is from the same target, filtering calculations using, for example, the following equations are performed on the distance and relative velocity data that have been determined as being from the same target.
[Relative velocity]=([Previous value]xc3x973+[Present value])/4
[Distance]=([Previous value]+[Present value])/2
The pairing process consists of two steps: pairing based on the past, for preferentially pairing up the peaks existing within the predicted frequency range where the target is expected to exist based on the position and velocity predicted from the past data, and new pairing for pairing up the peaks remaining after the completion of the pairing based on the past. In the pairing based on the past, if one or both of the peaks are temporarily nonexistent within the predicted range, extrapolation is performed for a predetermined period of time by assuming that the target is present at the predicted position. When the distance to the target is decreasing, up peaks at low frequencies tend to disappear, and the extrapolation performed in this case is called the down beat extrapolation.
The predicted values of the target data are calculated from the following equations by assuming that the previously calculated relative velocity is applicable to the present data.
[Distance]=[Previously calculated distance]+[Previously calculated relative velocity]xc3x97[Time]
[Relative velocity]xc3x97[Previously calculated relative velocity]
FIG. 1 shows the frequencies of a down peak 10 and up peak 12 changing with time when the distance to a target traveling in front decreases and then increases slightly, finally settling down to maintain a constant distance. The sum of the frequencies of the two peaks corresponds to the distance to the target, and the difference corresponds to the relative velocity.
Assume here that, as shown in FIG. 2, at time t1 the frequency of the up peak drops and the peak cannot be detected, whereupon the down beat extrapolation is initiated. As the distance is given by the sum of the two frequencies, if the scale is taken properly, the distance can be represented by a semi-dashed line, indicated by reference numeral 14, drawn between the two frequencies. As previously described, as the estimated position of the target is calculated by assuming that the relative velocity is constant during the down beat extrapolation, if the filtering calculations are performed, the estimated value 14 of the distance decreases substantially linearly, and the estimated frequency 16 of the down peak and the estimated frequency 18 of the up peak also decrease substantially linearly with essentially the same slopes. Accordingly, if the actual relative velocity decreases, decreasing the frequency difference, and the frequency of the down peak stops further decreasing, the disparity between the actual and estimated values increases and finally, at time t2, the down peak goes outside the predicted range and a new pairing is initiated. At time t3, if the up peak is detected here, since it is still outside the predicted range, the down beat extrapolation is initiated once again. Thereafter, at time t4, the down peak goes outside the predicted range, and the new pairing is initiated, but at time t5, the up peak goes outside the predicted range, and the down beat extrapolation is initiated once again.
In this way, the prior art has had the problem that, if the actual relative velocity changes by more than a certain value during the extrapolation, it takes a finite time until the output value comes to reflect the actual value.
A first object of the present invention is to increase the accuracy of radar measurements by quickly detecting the occurrence of mispairing, a mirror ghost, etc.
A second object of the present invention is to provide a radar data processing apparatus that can quickly recover if the actual relative velocity changes during extrapolation.
According to the present invention, there is provided a data processing apparatus for a millimeter-wave radar, which receives data concerning peaks appearing in a frequency spectrum of a beat signal produced by mixing a received signal with a portion of a transmitted signal frequency-modulated by a triangular wave increasing and decreasing alternately in a cyclic fashion, and which processes the peak data for the increasing and decreasing sections of the triangular wave for a plurality of angles, comprising: means for determining pairing between the peaks in the increasing section of the triangular wave and the corresponding peaks in the decreasing section thereof; means for calculating, from the frequencies of the paired peaks, a distance to each individual target and the relative velocity of the target; and means for determining an ineligible target based on the calculated relative velocity.
The apparatus further comprises means for determining whether each individual target is a stationary target or a moving target, based on the traveling speed of a vehicle equipped with the radar and the relative velocity of the target, and in one example, the ineligible target determining means determines that any moving target that, according to the calculated values of the distance and relative velocity, is supposed to be present in the vicinity of a stationary target is an ineligible target.
The apparatus further comprises means for determining an eligible target based on continuity with past data, and in one example, the ineligible target determining means determines that any target that, according to the calculated values of the distance and relative velocity, is expected to virtually collide with the eligible target is an ineligible target.
In another example, the ineligible target determining means determines that any target for which the calculated value of the relative velocity is an unlikely value is an ineligible target.
In still another example, when there are two moving targets exhibiting substantially the same motion according to the calculated values of the distance and relative velocity, the ineligible target determining means determines that the moving target located outward of the other target is an ineligible target.
The apparatus further comprises means for determining whether each individual target is a stationary target or a moving target, based on the traveling speed of the radar-equipped vehicle and the relative velocity of the target, and the ineligible target determining means determines that any moving target that is located outward of a stationary target according to the calculated values of the distance and relative velocity is an ineligible target.
According to the present invention, there is also provided a data processing apparatus for a millimeter-wave radar, which receives data concerning peaks appearing in a frequency spectrum of a beat signal produced by mixing a received signal with a portion of a transmitted signal frequency-modulated by a triangular wave increasing and decreasing alternately in a cyclic fashion, and which processes the peak data for the increasing and decreasing sections of the triangular wave for a plurality of angles, comprising: means for determining pairing between the peaks in the increasing section of the triangular wave and the corresponding peaks in the decreasing section thereof; means for calculating, from the frequencies of the paired peaks, a distance to each individual target and the relative velocity of the target; means for grouping together peaks substantially equal in frequency and distributed within a prescribed angle range, by determining that the peaks are due to reflections from the same target; and means for determining that, if the number of peaks belonging to the same group is smaller than a predetermined value, that the peaks belonging to the same group are ineligible peaks.
Preferably, the ineligible peak determining means determines that any peak having an intensity greater than a predetermined threshold value is an eligible peak even when the number of peaks belonging to the same group is smaller than the predetermined value.
According to the present invention, there is also provided a radar data processing apparatus comprising: means for checking continuity to determine whether previously obtained target data and currently obtained target data are data obtained from the same target; means for performing filtering calculations on the target data that has been determined as being data from the same target as a result of the continuity check; and means for prohibiting the filtering calculations from being performed for the calculation of the relative velocity of the target contained in the target data, if the currently obtained target data is data calculated from currently obtained actual measured values, and if the previously obtained target data is data calculated by extrapolation, not from actual measured values.
The reason that it takes a finite time to recover is that, as can be seen from the example of FIG. 2, if new pairing is done after extrapolation, the estimated value does not come close to the actual value because of the filtering calculations of the relative velocity. In view of this, in order to achieve quick recovery, provisions are made not to perform the filtering calculations of the relative velocity, if the current data is data obtained by new pairing, and if the previous data is data calculated by extrapolation.